EFFECT OF SHEAR STRESS ON PLATELET-PMN LEUKOCYTE INTERACTIONS

Abstract

A cone and plate viscometer, Coulter counter, and spectrophotometer were used to study platelet modulation of polymorphonuclear leukocyte (PMNL) function caused by controlled shear stress. Aggregation and release of the enzymes β-glucuronidase and lactate dehydrogenase (LDH) were observed. PMNL suspensions in buffer (1.0 × 10⁷ cells/ml, final concentration) did not show any aggregate formation or enzyme release at shear stresses below 150 dynes/cm² for an exposure time of 1 minute. However, supernatant plasma from sheared platelets initiated PMNL aggregation and β-glucuronidase release at moderate shear stresses (150 dynes/cm² for 1 minute). These stress-induced alterations were compared with chemotactic factor and calcium ionophore A23187 induced functional changes. LDH release was less than 3% in all the experiments indicating little overt lysis. The shear-induced enzyme release was enhanced by cytochalasin B and heparinized samples showed greater effects than citrated samples. The use of a cyclooxygenase inhibitor (acetylsalicyclic acid, 50 μM) did not suppress the aggregation of PMNLs after shear. However, preincubation with lipoxygenase inhibitors (nordihydroguaiaretic acid, 10 μM, and U-60257, 10 μM) suppressed aggregation and enzyme release. The formation of arachidonic acid metabolites activated by shear stress was documented by reversed phase-high pressure liquid chromatography. Thus, an interaction between C-12 and C-5 lipoxygenase enzymes can promote the formation of leukotriene B₄ and these data strongly support the possibility of a cooperation between platelet and PMNL arachidonic acid metabolites in shear-induced PMNL functional changes.